This proposal is designed to exploit the autologous mixed lymphocyte responses (AMLR) as an in vitro analog of afferent immune function in recipients of renal and cardiac allografts. Twenty-three long-term recipients of related renal allografts will be evaluated to elucidate the functional lesion responsible for the observed absence of autologous reactivity in these individuals. Specific experiments are proposed to evaluate the ability of recipient E+ and E- lymphocytes to respond to and stimulate cells from an HLA-identical sibling. AMLR cultures established with isolated T-cell subpopulations are proposed for the detection of cells capable of suppressing the AMLR by lymphocytes from an HLA-matched sibling. Additional experiments using these recipients will evaluate other T-cell functions that have been shown to be closely correlated with auto-reactive T-cells. These include responsiveness to Con A stimulation, the ability to form rosettes with autologous erythrocytes, and the expression of a cell surface antigen defined by a novel monoclonal antibody, Ku-ET69. Relevant correlations with afferent immune function will be provided by experiments that evaluate the capacity of recipient lymphocytes to respond in an antigen presentation system and to generate cytolytic T-cells against hapten-modified autologous T-cells. Serial monitoring of recent renal and cardiac allograft recipients for reactivity in the AMLR will determine any existing correlation between this afferent response and allograft status, immunosuppressive therapy, OKT4+/OKT8+ cell ratios, and percentage of Ku-ET69+ cells. Finally, assays are proposed to further characterize a T-helper cell-specific monoclonal antibody (Ku-ET69) that specifically blocks the AMLR. Experiments will determine the ability of Ku-ET69 to block such AMLR-associated activities as Con A stimulation, antigen presentation and autologous E-rosette formation. These studies will provide important information regarding afferent immune functions that are associated with the development of allograft acceptance. Deliberate pertubation of these functions may improve the future success of transplanting HLA-nonidentical grafts.